The Impact of Distributed Energy Resources on Distribution-system Protection

The introduction of distributed energy resources (DER) in radial parts of the grid, at low and mediumvoltage levels, may adversely impact the operation of the protection. Synchronous and induction generators contribute to the fault current, creating a second path next to the fault-current contribution from the grid. This may lead to fail-to-trip as well as incorrect trip of protection based on overcurrent. The so-called hosting-capacity method was introduced for quantifying the impact of DER on voltage quality. The hosting capacity is obtained by comparing a voltage-quality of performance index with an objective for what is acceptable. This method is extended to distribution-system protection by defining the following limits: · The need to change current settings · The need to add additional time delay · The need for directional protection. Both quantitative and qualitative studies have been performed. The need to change settings may already arise for small levels of DER penetration, depending on the existing settings. However, only large penetration levels require additional time delay of directional protection. -